Response of cyanobacterial mats to nutrient and salinity changes

Cyanobacterial mats (CBM), complex assemblages of cyanobacteria, bacteria and algae, are important ecosystem components of oligotrophic marshes in limestone-based regions of the Caribbean. We conducted a mesocosm experiment and evaluated the response of CBM to factorial combinations of low, medium and high phosphorus, nitrogen and salinity. Changes in composition of the main species groups of cyanobacteria and algae, primary production, cellular nutrients and enzymatic activities were recorded as response variables. The redundancy analysis with concentrations of P, N and salinity as explanatory variables showed that the primary production of CBM and the amount of phytoplankton expressed as Chl a were best explained by concentration of P, with less significant positive effect of N and a negative effect of salinity. Abundance of green algae and Chroococcales was positively correlated with increasing concentrations of P and N and reached 27.6% and 21.9%, respectively, in high P and high N treatment at the end of experiment. N₂-fixation averaged 75 and 175 nmol C₂H₄ cm⁻² min⁻¹, at low nitrogen and medium or high P, respectively, and it was negatively correlated with nitrogen concentration and positively correlated with abundance of a group of heterocytous cyanobacteria from genus Nostoc. At low N concentrations, increasing P concentrations supported higher N₂-fixation. Activity of the alkaline phosphatase, APA, was negatively correlated with P and salinity and positively with N. We also found a significant negative correlation between the APA activity and the P content of the mat. At high P and N concentrations, the mats were impacted by grazing, had a tendency to disintegrate and become shaded out by a massive growth of phytoplankton. We confirmed an overall negative effect of nutrient increase on CBM.     

Widespread distribution and identification of eight novel microcystins in antarctic cyanobacterial mats

The microcystin (MC) content and cyanobacterial community structure of Antarctic microbial mat samples collected from 40 ponds, lakes, and hydroterrestrial environments were investigated. Samples were collected from Bratina Island and four of the Dry Valleys, Wright, Victoria, Miers, and Marshall. Enzyme-linked immunosorbent assays (ELISAs), liquid chromatography-mass spectrometry (LC-MS), and protein phosphatase 2A (PP-2A) inhibition assays resulted in the identification of low levels (1 to 16 mg/kg [dry weight]) of MCs in all samples. A plot of indicative potencies of MCs (PP-2A inhibition assay/ELISA ratio) versus total MCs (ELISA) showed a general decrease in potency, as total MC levels increased, and a clustering of values from discrete geographic locations. LC-tandem MS analysis on selected samples identified eight novel MC congeners. The low-energy collisional activation spectra were consistent with variants of [D-Asp(3)] MC-RR and [D-Asp(3)] MC-LR containing glycine [Gly(1)] rather than alanine and combinations of homoarginine [hAr(2)] or acetyldemethyl 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid (acetyldemethyl ADDA) [ADMAdda(5)] substitutions. Nostoc sp. was identified as a MC producer using PCR amplification of a region of the 16S rRNA gene and the aminotransferase domain of the mcyE gene. Automated ribosomal intergenic spacer analysis (ARISA) was undertaken to enable a comparison of cyanobacterial mat community structure from distant geographical locations. Two-dimensional multidimensional scaling ordination analysis of the ARISA data showed that in general, samples from the same geographic location tended to cluster together. ARISA also enabled the putative identification of the MC-producing Nostoc sp. from multiple samples.     

Calcium carbonate precipitation in cyanobacterial mats from sandy tidal flats of the North Sea

Precipitated calcium carbonate was found in annual cyanobacterial mats developing on the beaches of the North Sea barrier island Schiermonnikoog (the Netherlands). A variety of different calcium carbonate morphs were found in the cyanobacterial mucous secretions and identified by light- and scanning electron microscopy and X-ray diffraction. Most of the calcium carbonate seemed to be associated with degrading extracellular polymer. It is conceived that supersaturation of calcium carbonate resulted from the periodic evaporation of the mats and from the release of calcium from the cyanobacterial mucous as a result of its degradation. The analysis of the carbon stable isotopic composition of the calcium carbonate showed only a slight depletion of ¹³C, indicating that it did not in major part originated from the decomposition of organic matter. The δ¹⁸O values of the calcium carbonate confirmed the temperature differences between spring and summer but excluded the possibility that excessive evaporative events controlled precipitation. The precipitation of calcium carbonate could represent a potential factor enhancing the stabilization of intertidal siliciclastic sediments through cementing the sand. The discovery of massive calcium carbonate precipitation in these cyanobacterial mats was unexpected and hitherto unknown.     

Recent climatic changes recorded by the salinity of pore waters in the Dead Sea sediments

A new, flow-through benthic corer is described and compared to other commonly used coring methods. The new corer compares favorably with diver coring and is superior to coring with a ball-type, check valve corer, based on recovery of meiofauna, macrofauna, and particle bound hydrocarbons. Check valve corers yielded the most variable results. The new corer may be used to efficiently obtain samples of surface sediments from shallow (<6 m) water, where a reasonably stable working platform is available.     

Transfer function between surface sediment diatom assemblages and sea-surface temperature and salinity of the Labrador Sea

Q-mode factor analysis (CABFAC) of 38 diatom species in 66 surface sediment samples from the Labrador Sea allowed the definition of six assemblages explaining 95.69% of the total variance. The first assemblage (40.12% of the total variance) is represented by Thalassiothrix longissima, a species characteristic of the Irminger Current and associated with the West Greenland Current. The second assemblage (34.52% of the total variance) is represented by Thalassiosira gravida (resting spores), a cold water species associated with the Labrador Current. A third assemblage (11.43% of the variance) represented by Chaetoceros spp. is concentrated in the northeastern section of the Labrador Sea and associated with upwelling and high productivity. The fourth, the fifth and the sixth assemblages, represented, respectively, by Coscinodiscus marginatus, Coscinodiscus oculus iridis, and Coscinodiscus divisus, and Nitzschia frigida, are less significant and account, respectively, for 4.95, 2.62 and 2.04% of the total variance. Transfer functions derived by relating factor assemblages to surface water temperature and salinity (August and February) give standard errors of estimate of ±0.93°C (August) and ±0.64°C (February) for temperature, and of ±0.58‰ (August) and ±0.45‰ (February) for salinity. High correlations between the measured and estimated parameters confirm the validity of the paleoecological equations for the reconstruction of the Labrador Sea paleoclimate.     

PCR analysis of the distribution of unicellular cyanobacterial diazotrophs in the Arabian Sea

An oligonucleotide primer, NITRO821R, targeting the 16S rRNA gene of unicellular cyanobacterial N2 fixers was developed based on newly derived sequences from Crocosphaera sp. strain WH 8501 and Cyanothece sp. strains WH 8902 and WH 8904 as well as several previously described sequences of Cyanothece sp. and sequences of intracellular cyanobacterial symbionts of the marine diatom Climacodium frauenfeldianum. This oligonucleotide is specific for the targeted organisms, which represent a well-defined phylogenetic lineage, and can detect as few as 50 cells in a standard PCR when it is used as a reverse primer together with the cyanobacterium- and plastid-specific forward primer CYA359F (U. Nubel, F. Garcia-Pichel, and G. Muyzer, Appl. Environ. Microbiol. 63:3327-3332, 1997). Use of this primer pair in the PCR allowed analysis of the distribution of marine unicellular cyanobacterial diazotrophs along a transect following the 67 degrees E meridian from Victoria, Seychelles, to Muscat, Oman (0.5 degrees S to 26 degrees N) in the Arabian Sea. These organisms were found to be preferentially located in warm (>29 degrees C) oligotrophic subsurface waters between 0 and 7 degrees N, but they were also found at a station north of Oman at 26 degrees N, 56 degrees 35'E, where similar water column conditions prevailed. Slightly cooler oligotrophic waters (<29 degrees C) did not contain these organisms or the numbers were considerably reduced, suggesting that temperature is a key factor in dictating the abundance of this unicellular cyanobacterial diazotroph lineage in marine environments.     

Physiological response of the unicellular green alga Chlorococcum submarinum to rapid changes in salinity

Cell volumes and intracellular concentrations of major solutes of Chlorococcum submarinum were determined before and after salinity shocks. Cells were found to shrink in size by about 30% following changes from 0.1 to 0.5 M NaCl, there was a transitory increase in sodium concentration and more permanent increases in concentrations of potassium, proline and glycerol (the major osmolyte). Conversely, cells doubled in size after the reciprocal downshock, there was rapid loss of about 70% of the cells' glycerol to the medium, a much smaller loss of cellular potassium and a steady disappearance of proline from the cells. The respiratory and photosynthetic responses to salinity fluctuations were also studied. Salinity downshocks stimulated respiration by 30% and inhibited photosynthesis by 16% within 5 min, but within 2 h these rates were identical to control rates. Upshocks caused a slight inhibition of respiration, but decreased photosynthesis by 40% within 5 min and recovery took 2 h. Downshocks had little effect on chlorophyll fluorescence, however, Fo strongly increased and both Fm and Fv/Fm declined within 5 min of salinity increases. This is consistent with a decrease in efficiency of PS2. Ecological and metabolic implications of the results are discussed.Abbreviations DMSO dimethyl sulphoxide - Hepes N-[2-hydroxyethyl]piperazine-N-2-ethane sulphonic acid - TCA trichloroacetic acid - Tris tris[hydroxymethyl]aminoethane     

Metal biosorption by two cyanobacterial mats in relation to pH, biomass concentration, pretreatment and reuse

The pH-dependent metal sorption by Oscillatoria- and Phormidium-dominated mats was effectively expressed by the Hill function. The estimated Hill functions can fruitfully predict the amount of metal sorbed at a particular initial pH. Pretreatment of biomass with 0.1 mmol L⁻¹ HCl was more effective than pretreatment with CaCl₂, HNO₃, NaOH, and SDS in enhancing metal sorption ability of the biomass. Desorption of metal ions in the presence of 100 mmol L⁻¹ HCl from metal-loaded mat biomass was completed within 1 h. After six cycles of metal sorption/desorption, sorption decreased by 6-15%. Only 6% and 11% of the biomass derived from the Oscillatoria sp.- and Phormidium sp.-dominated mats was lost during the cycling. The cyanobacterial mats seem to have better potential than several biomass types for use in metal sorption from wastewaters as they are ubiquitous, self-immobilized, and have good reusability.     

Spatial distribution of ectomycorrhizal mats in coniferous forests of the Pacific Northwest, USA

Ectomycorrhizal mats in forest soils have a wide global distribution and have been noted as potentially important elements in forest soil nutrient cycling. To elucidate the relationship between ectomycorrhizal mats and their environment, we undertook field studies and spatial analyses of mat distributions at different spatial scales.We used two experimental approaches to study mat-forming ectomycorrhizal fungi in coniferous forests of the Pacific Northwest in the United States. In the first approach, ectomycorrhizal mats and other forest floor features were mapped in 2 × 10 m plots and digitized into a geographical information system (GIS) for spatial pattern analysis. In order to examine larger-scale phenomena, a second approach involving other sites was taken; soil cores were taken along 30-m transects, and distance to the closest living potential host tree was calculated for each core.Mat patterns were studied at two scales: (1) within-stand level (i.e. variability attributed to distribution of other mat species, forest floor attributes, and understory vegetation); and (2) stand level (i.e. variability expressed along a successional gradient). Mat distribution was influenced by: (1) the proximity of one mat to another; (2) the distance from the mat to the closest living tree; (3) the density of living trees in a stand; and (4) the successional stage of the stand.Although GIS analysis indicated that mats of different morphologies did not physically overlap, there was a tendency for clustering of mats. No apparent correlations were observed between forest floor features and mats located within the 2 × 10 m grids. On the scale of tens of meters, mats decreased with distance from the closest potential host tree. Spatial patterns of mat distributions in harvested sites suggest that these mats may persist at least 2 years after their host trees have been cut. For Gautieria mats, total mat area, size, and frequency differed with stand age.This study has demonstrated the importance of both spatial scaling and forest stand age when the natural distribution of mycorrhizal fungi is examined. Results suggest the need for mat research directed at higher-order scales (e.g. stand and watershed) that will provide accurate information for managing forests to ensure their survival and normal function. ei]J H Graham     

Characterization of metal-binding bioflocculants produced by the cyanobacterial component of mixed microbial mats.

Mixed-species microbial mats that were dominated by the cyanobacterium Oscillatoria sp. and contained heterotrophic and purple autotrophic bacteria were constructed for specific bioremediation applications. When the mats were challenged with metals, production and secretion of metal-binding extracellular polysaccharide bioflocculants were observed. The concentration of these negatively charged polysaccharides was correlated with the removal of manganese from the water column beneath a surface microbial mat. Bioflocculants from an Oscillatoria sp. that was isolated from the mat were collected and concentrated for characterization. A chromatographic analysis revealed a heterogeneous population of polysaccharides with respect to charge density and molecular size. The subpopulation of polysaccharides which exhibited the highest level of flocculating activity was polyanionic and had a molecular weight of more than 200,000. A glycosyl analysis of the bioflocculants revealed the presence of galacturonic acid (2.2%) and glucuronic acid (1.86%). The presence of these components, which were negatively charged at the pH levels generated by the mats during photosynthesis (pH > 7.5), may account for the metal-binding properties of the mats.     

Invasibility in a spatiotemporally fluctuating environment is determined by the periodicity of fluctuations and resident turnover rates

The ability of a species to invade a community is influenced by the traits of the invader, the resident community and the environment. However, qualitative generalizations are possible. Using a model of perennial plants in a spatiotemporally fluctuating environment, we find that fluctuating environments may be more or less invasible than static environments. Invasibility is strongly dependent on the interaction of the difference in turnover rates of resident and invader populations and the rate of temporal change of the environment. If resident population turnover is faster than the invader's, then invasibility is an initially positive, decreasing function of the period temporal variation, such that invasibility is increased by rapid temporal fluctuations but slightly reduced in slowly fluctuating environments. If resident turnover is slower than the invader's, then invasibility is an initially negative, increasing function of temporal period, such that invasibility is reduced in rapidly changing environment facilitated by slow temporal fluctuations. These results are explained by the relative abilities of resident and invader populations to successfully respond to environmental variation at different temporal scales.     

Diurnal and seasonal variations of nitrogen fixation and photosynthesis in cyanobacterial mats

In situ measurements of nitrogenase activity and photosynthesis were performed simultaneously in cyanobacterial mats of intertidal sand flats of the Southern North Sea. Two types of cyanobacterial mats, which differed in species composition and biomass content, were investigated. The measurements were done monthly during 3 years to detect seasonal variations of nitrogen fixation and photosynthesis. Diurnal variations were investigated as well. The results showed that (i) freshly colonized sediment with the cyanobacteriumOscillatoria limosa as the dominant organism revealed the highest specific nitrogenase activities (ii) nitrogenase activities were highest in spring and summer, when mat development was initiated and (iii) diurnal fluctuations of nitrogenase activity indicated that it occurred temporally separated from oxygenic photosynthesis.     

Subcellular distribution of enzymes determined by rapid digitonin fractionation of isolated hepatocytes

Conditions were determined for rapid separation of cytosolic and mitochondrial compartments by digitonin fractionation of rat hepatocytes. The minimum time required for separation of mitochondrial and cytosolic enzyme markers decreased rapidly with increasing temperature. Kyro EOB, a non-ionic detergent, increases the release of cytosolic enzymes, particularly at lower temperatures. Experimental procedures are described for greater than 90% release of cytosolic enzymes and less than 2% release of mitochondrial enzymes in 3s. By using appropriate concentrations of digitonin and Kyro EOB in a fractionation medium maintained at 1°C and a minimum time of exposure to the medium, nearly separate patterns of release were obtained for enzyme markers for the cytosol, mitochondrial matrix and mitochondrial intermembrane space. The distribution of enzymes that exist in more than one of these compartments was quantified by comparing their rates of release with those of marker enzymes. The cytosol/mitochondrial-matrix distributions for such enzymes in hepatocytes from starved rats were 16%/84% for aspartate aminotransferase, 34%/66% for fumarase and 77%/23% for ATP citrate lyase. In hepatocytes from rats that were induced to synthesize ATP citrate lyase by starvation and re-feeding, the ratio had increased to 95%/5%. The maximum cytosol/intermembrane-space ratio for adenylate kinase was 8%/92%. A procedure is also described for treating commercial digitonin that increases its solubility in water from about 1mg/ml to more than 800mg/ml.     

Effect of salinity changes on the bacterial diversity, photosynthesis and oxygen consumption of cyanobacterial mats from an intertidal flat of the Arabian Gulf

The effects of salinity fluctuation on bacterial diversity, rates of gross photosynthesis (GP) and oxygen consumption in the light (OCL) and in the dark (OCD) were investigated in three submerged cyanobacterial mats from a transect on an intertidal flat. The transect ran 1 km inland from the low water mark along an increasingly extreme habitat with respect to salinity. The response of GP, OCL and OCD in each sample to various salinities (65 per thousand, 100 per thousand, 150 per thousand and 200 per thousand) were compared. The obtained sequences and the number of unique operational taxonomic units showed clear differences in the mats' bacterial composition. While cyanobacteria decreased from the lower to the upper tidal mat, other bacterial groups such as Chloroflexus and Cytophaga/Flavobacteria/Bacteriodetes showed an opposite pattern with the highest dominance in the middle and upper tidal mats respectively. Gross photosynthesis and OCL at the ambient salinities of the mats decreased from the lower to the upper tidal zone. All mats, regardless of their tidal location, exhibited a decrease in areal GP, OCL and OCD rates at salinities > 100 per thousand. The extent of inhibition of these processes at higher salinities suggests an increase in salt adaptation of the mats microorganisms with distance from the low water line. We conclude that the resilience of microbial mats towards different salinity regimes on intertidal flats is accompanied by adjustment of the diversity and function of their microbial communities.     

Amino acid signatures of salinity on an environmental scale with a focus on the Dead Sea

The increase of the acidic nature of proteins as an adaptation to hypersalinity has been well documented within halophile isolates. Here we explore the effect of salinity on amino acid preference on an environmental scale. Via pyrosequencing, we have obtained two distinct metagenomic data sets from the Dead Sea, one from a 1992 archaeal bloom and one from the modern Dead Sea. Our data, along with metagenomes from environments representing a range of salinities, show a strong linear correlation (R² = 0.97) between the salinity of an environment and the ratio of acidic to basic amino acids encoded by its inhabitants. Using the amino acid composition of putative protein‐encoding reads and the results of 16S rRNA amplicon sequencing, we differentiate recovered sequences representing microorganisms indigenous to the Dead Sea from lateral gene transfer events and foreign DNA. Our methods demonstrate lateral gene transfer events between a halophilic archaeon and relatives of the thermophilic bacterial genus Thermotoga and suggest the presence of indigenous Dead Sea representatives from 10 traditionally non‐hyperhalophilic bacterial lineages. The work suggests the possibility that amino acid bias of hypersaline environments might be preservable in fossil DNA or fossil amino acids, serving as a proxy for the salinity of an ancient environment. Finally, both the amino acid profile of the 2007 Dead Sea metagenome and the V9 amplicon library support the conclusion that the dominant microorganism inhabiting the Dead Sea is most closely related to a thus far uncultured relative of an alkaliphilic haloarchaeon.     

Spatial and temporal distribution of copepod communities in the Adriatic Sea

The distribution of planktonic copepods in the Adriatic Seahas been analyzed on the basis of 132 samples collected at 35fixed stations during 4 seasonal cruises. A total of 127 specieshave been determined and 3 characteristic copepod communitieshave been identified. The distribution of copepod species hasbeen found to reflect the dual physiognomy of the Adriatic.The shallow northern section is characterized by high densityvalues, low species diversity, and the dominance of speciesbelonging to the estuarine and coastal communities. The relativelydeep waters of the southern section are characterized by lowdensity values, high species diversity, and the presence ofmany species belonging to the upper, middle, and lower zonesof the oceanic community. Temporal variations in the horizontalspread of these 3 communities are discussed in relation to seasonalcycles in abundance, vertical migration patterns, and the currentregime in the Adriatic.     

Spatial and temporal distribution patterns of Cladocera in the Argentine Sea

In the marine sciences, continuous monitoring systems have been regarded as very useful tools to provide continuous high frequency measurements of many parameters. We analyse here a high frequency time series of temperature measurements recorded every 10 min between 1997 and 2004 in the macro tidal Seine estuary (France) by a Marel buoy, an automatic monitoring network for littoral environment. We have adapted multi-scale data analysis methods to deal with the many missing values present in the time series. A power spectral density analysis is performed over time scales spanning 5 decades, from 20 min to more than 7 years. A scale invariant behaviour of the form with β = 2.2 is revealed for scales below 5 h. Over this scaling range, we have performed structure functions analysis, and shown that the Seine river temperature data exhibit turbulent-like intermittent properties, with multifractal statistics. The multifractal exponents obtained possess some similarities with passive scalar turbulence results. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.